Sausage casings of regenerated cellulose are well known in the art. Cellulosic casings are of several different types and sizes to accommodate the different categories of food products to be prepared. These casings also are provided in supported or unsupported form, the supported casings, commonly referred to as "fibrous casings", having a fibrous support web embedded in the casing wall.
For convenience in handling, casings which may be 20 to 70 m or more in length are shirred and compressed to produce what is commonly referred to as "shirred casing sticks" which measure about 20 cm to about 70 cm in length.
Fibrous casings are commonly used in the preparation of food products such as salami and bologna sausages, meat loaves, cooked and smoked ham and smoked pork butts and the like. These casings are produced in stuffed diameter sizes from about 50 mm to about 200 mm or larger.
Generally, a fibrous casing contains about 25% to 35% of a polyol (such as glycerine) based on the dry weight of the cellulose in the casing as a humectant and softening agent. The casing also contains about 17% to 35% moisture based on total weight of the casing. At this moisture level the fibrous casing can be shirred and will contain enough moisture to permit stuffing the casing without adding further moisture. The preferred moisture content of the fibrous casing depends upon the type of product to be stuffed in the casing. For example, for boneless hams, a preferred range is from about 20% to about 26% moisture based on total casing weight whereas for a meat emulsion the preferred range is from about 17% to about 23%. In any event, it should be appreciated that a fibrous casing which in its as-sold condition is ready for stuffing contains an appreciable amount of both polyols (e.g., glycerine) and moisture.
For purposes of present day automatic stuffing machines it is preferred to provide a shirred stick containing as long a length of casing as possible. However, for various reasons it is not always possible to provide a single continuous length of casing long enough to produce a shirred stick. Accordingly, it is common for a casing manufacturer to join together shorter lengths of casings so that each shirred stick may contain one or more splices.
Having one or more splices in a length of shirred casing is not desirable. This is because the splices interfere with the stuffing procedure, especially in present day high speed automatic stuffing machines. These machines subject the casing to considerable longitudinal and transverse stresses which cause the splice to fail. Consequently, it is not uncommon to interrupt the stuffing operation to clear and remove the splice before it is stuffed.
The problem is particularly acute when using a stuffing method which requires circumferentially stretching the casing just prior to the introduction of the foodstuff into the casing. Reference is made to U.S. Pat. No. Re. 30,390 for a description of a conventional automatic stuffing machine which circumferentially stretches the casing prior to stuffing. As disclosed in U.S. Pat. No. Re. 30,390, casing is deshirred and drawn forward from a shirred supply by the introduction of the food product into the casing. As the casing deshirrs, it passes over a so-called "sizing disc" which has an outer periphery larger in circumference than the unstretched inner periphery of the casing. This causes the casing to stretch circumferentially as much as 15% as it traverses the disc. Moreover, the act of drawing the casing over the disc and stretching it creates a drag or "holdback" on the casing which retards the forward progression of the casing and longitudinally stresses the casing.
A splice in the casing causes several problems. If a pressure sensitive adhesive tape used in making the splice has a low extensibility, it may not be able to accomodate the circumferential stretching of the casing and may break as the splice passes over the sizing disc. If the tape does not break, its lack of extensibility can prevent it from passing over the disc so as to slow or even stop the forward progression of the casing over the disc. Retarding the forward progress of the casing in this fashion increases the drag or holdback on the casing. The resulting increase in longitudinal stress can cause either an adhesive or a cohesive failure of the tape or the casing may break. In an adhesive failure, the tape peels from the casing, whereas in a cohesive failure the tape adhesive fails in shear, leaving a portion of the adhesive adhered to the casing and a portion adhered to the tape backing. In either case, the splice opens.
If the tape is so extensible that it can stretch sufficiently to pass over the disc, the splice may fail in another mode. This is because the drag created as the splice passes over the sizing disc causes the tape to stretch in the direction of casing movement. This stretch in the direction of casing movement pulls apart the adjacent spliced together ends of the casing and creates a gap between the adjacent casing ends which is bridged by the stretched tape. This may be objectionable because it exposes the food within the casing to the adhesive which typically is not approved for direct food contact.
Accordingly, an acceptable pressure sensitive splice tape for use with a shirred fibrous casing must satisfy several requirements. The tape, of course, must have an adhesive component that provides good adherence to the polyol and moisture containing casing. The tape also must be extensible so as to withstand the rigors of shirring and accommodate the circumferential expansion of the casing of up to 15% or more to permit the splice to clear a sizing disc during stuffing; and the tape must not be so extensible that it permits the adjacent ends of the spliced casings to pull apart when the casing is subjected to a drag or holdback which retards the forward progression of the casing.
An ideal splicing tape for cellulosic casing would adhere to the casing by pressure alone, would be capable of accommodating up to 15% or more circumferential stretching of the casing and would resist the longitudinal (machine direction) tensile forces tending to pull the splice apart. Thus, the stretch characteristics of an ideal splicing tape must be anisotropic in that it must be extensible in its longitudinal direction and relatively unextensible in its transverse direction. It is important to note that when the splice tape is in position and holding the joined ends of casing together, the tape is oriented so that in its longitudinal direction the tape accomodates the circumferential stretch of the casing whereas in its transverse direction, the tape resists the forces tending to longitudinally pull apart the joined ends of casing.
Accordingly, an object of the present invention is to provide an anisotropic pressure sensitive adhesive tape suitable for use in joining lengths of fibrous cellulosic food casings.
Another object is to provide such a tape suitable for making a stuffable splice.
Still another object is to provide a spliced fibrous cellulosic casing formed by an anisotropic pressure sensitive adhesive tape which permits the joined together ends of the fibrous casings to stretch circumferentially by 15% or more and which resists the longitudinal separation of the joined ends of the casing.
A further object of the present invention is to provide an anisotropic pressure sensitive tape.
Yet another object of the present invention is to provide an anisotropic pressure sensitive adhesive tape wherein the extensibility of the tape in its longitudinal direction is 10 to 20 times its extensibility in a transverse direction.